Certain disc brake units for railway vehicles are provided with a latch which is pivotally mounted on the brake shoe lining carrier having a dovetail groove or slot mortise for accommodating a matching dovetail tenon carried by the brake shoe backing plate. After the brake shoe lining is mounted to the carrier, the pivoted latch is moved to its locked position in which holes in the two locking lugs become aligned with a hole formed in the free end of the pivotal latch. In the past, the latch was locked by inserting a latch locking pin through the aligned holes. The latch locking pin had a configuration similar to a bobby hair pin having a bight portion from which extended a first straight leg and a second serpentine leg. Normally, the straight leg is vertically inserted into the hole in the top lug and then thrust through the holes in the pivotal latch and bottom lug. The serpentine leg frictionally engages the outer surfaces of the two lugs to maintain the pin in place. Generally, the hair pin operated satisfactorily if it was properly and initially inserted into the hole in the top lug of the brake shoe head carrier. However, it has been found that maintenance workers and/or other railroad personnel have not followed the instructions and procedures as outlined in the manufacturer's operating manual. For one reason or another, the bobby hair pins have been installed in a reverse or upside-down manner. That is, the straight leg was being initially inserted into the hole of the bottom lug and then pushed through the holes in the pivotal latch and top lug. While the brake shoe appears to be positively locked to the brake head carrier, it has been discovered that when the reversely installed hair lock pin falls out, the brake shoe falls off of the brake head carrier. That is, the vibrational and gravitational forces experienced by the railway vehicles during the normal course of travel have a tendency to loosen the reversely inserted pin and cause it to drop out of the holes. The loss of the lock pin permits the pivotal latch to move or swing to its unlocked position so that the brake shoe falls off the brake head so that the braking action on the brake unit is rendered inefficacious. It will be appreciated that the loss of brake shoe can cause severe damage to brake unit and can jeopardize the safe operation of the railway vehicle.